Integrated circuits (ICs), such as, ultra-large scale integrated (ULSI) circuits, can include as many as one million transistors or more. The ULSI circuit can include complementary metal oxide semiconductor (CMOS) field effect transistors (FET). As the critical dimensions of ULSI circuits become smaller and smaller, transistor drive current is critical in determining overall integrated circuit speed and performance.
One of the factors that affects transistor drive current is the device architecture used in the transistor. In concurrent integration technology, CMOS FET (Complementary Metal-Oxide-Semiconductor Field-Effect Transistor) device architecture is typically considered to be dominant. CMOS FET architecture, however, has some limitations. First, the thickness of the gate dielectric is non-scalable. When the gate dielectric or gate oxide thickness is reduced to below 15.ANG., significant leakage current occurs due to a direct tunneling mechanism (i.e., charge carriers tunnel through the thin trapezoid potential barrier of gate oxide). The severe gate leakage current makes the MOS gate less capacitive but more resistive, therefore degrading the current drive due to a smaller amount of charge induced in the inversion channel. Second, MOSFETs are uni-polar devices. As such, only one type of carrier (either electron or hole) contributes to the channel conduction current, limiting the current drive capability.
In contrast, the Bipolar Junction transistor (BJT), used widely in the early stage of integrated circuit history, provides larger current drive capability due to its bipolar nature. That is, both types of charge carriers (i.e., electrons and holes) contribute to the current conduction. However, the BJT requires a relatively large amount of substrate area compared to MOSFETs. Accordingly, BJTs are not significantly utilized in ultra-large scale integration (ULSI) because of its large area consumption for a single device or transistor.
Thus, there is a need for a transistor architecture that combines the advantages of MOSFETs and BJTs, while attempting to avoid the disadvantages of both types of devices. Even further, there is a need for utilizing the direct tunneling leakage current through the ultra-thin gate dielectric as the base injection current for a lateral bipolar junction transistor built underneath the gate stack.